A flexible polyurethane foam is used for various applications, and one obtained by reacting a polyol compound and a polyisocyanate compound in an open system (slab method) and one obtained by reacting them in a closed system (molding method) are known. The flexible polyurethane foam obtained by the reaction in an open system is used, for example, for mattresses, beddings e.g. cushions for a sofa, or furniture. Further, the flexible polyurethane foam obtained by the reaction in a closed system is used, for example, for sheet cushions of a vehicle or sheet back materials.
The reaction of the polyol compound with the polyisocyanate compound is carried out in the presence of a urethane-forming catalyst, a blowing agent and a foam stabilizer, and as the foam stabilizer, a silicone foam stabilizer is widely used. For example, a flexible polyurethane foam using a dimethylpolysiloxane-polyoxyalkylene copolymer as the foam stabilizer is known (Patent Document 1).
However, since the silicone foam stabilizer contains a volatile organic compound (VOC), it may cause e.g. generation of an odor or drawbacks of electronic components. Further, in a case where microbes are supported on the flexible polyurethane foam and used for waste water disposal, a chemical oxygen demand (COD) may be increased by the silicone foam stabilizer. Further, in a production of the flexible polyurethane foam, since the unit price of the silicone foam stabilizer is generally the highest in raw materials, the economical efficiency tends to be low.
For an application for a sound insulting material, as a process for producing a polyurethane foam without using a silicone foam stabilizer, a process of using a polyether polyol having a molecular weight distribution within a range of from 1.02 to 1.2 and having a primary hydroxy group as a terminal group, is disclosed (Patent Document 2). However, since the obtained polyurethane foam has a density of at least 80 kg/m3, cushions properties are lost, and it tends to be hardly applied to mattresses, beddings e.g. cushions for a sofa, or furniture, which are applications of the flexible polyurethane foam obtained by a common reaction in the open system.
In the case of the closed system, as a process for producing the flexible polyurethane foam without using a silicone foam stabilizer, a process of using a polyol compound which is obtained by ring-opening polymerization of propylene oxide with an initiator by using a double metal cyanide complex catalyst (DMC catalyst), and further, ring-opening polymerization of ethylene oxide at its terminals by an alkali metal compound catalyst or a phosphazenium complex, is disclosed (Patent Document 3). However, generally, in the case of a reaction in the closed system, the foaming state is controlled so that the volume of the obtainable flexible polyurethane foam is larger than that of a mold for closing. Therefore, the reaction conditions are different from the case of foaming in the open system, and the conditions in the closed system cannot be applied as they are to the open system.
From the above, a strategy capable of producing a flexible polyurethane foam without using a silicone foam stabilizer in the open system is desired.    Patent Document 1: JP-A-2001-200028    Patent Document 2: JP-A-2005-301000    Patent Document 3: WO2006/054657